1. Field of the Invention
The present invention relates to an optical apparatus such as a digital camera, a video camera, a digital still camera, a television camera, and an interchangeable lens including a focus detection sensor for automatically focusing on an object.
2. Description of the Related Art
With a television auto focusing (TVAF) function in a video camera and a television camera, a video signal from an image sensor such as a charge-coupled device (CCD) is captured while a focusing lens is moved in a small amount to determine a focusing direction according to the difference in contrast values obtained before and after moving the focusing lens.
In such a TVAF system, when a focusing lens is disposed at a position close to an in-focus position, the focusing lens can immediately enter an in-focus state. However, in the case where the degree of blurring is high, it is necessary for a user to determine an in-focus position only after moving the focusing lens up to an end of a focusing lens movable range. Thus, the video image becomes unsightly for the user.
Thus, in a significantly defocused state, the contrast is very low, and a user cannot determine a focusing direction. Accordingly, in this case, it is necessary for a user to move the focusing lens to an infinitely distant end or a closest end to look for a position at which a contrast signal of a level is higher than a predetermined level. During this operation, the user is required to watch unfocused images, which causes the user to feel uncomfortable.
Meanwhile, a digital still camera employs a passive focus detection sensor as an auto focusing mechanism. A passive focus detection sensor can detect the difference between two images separated by a separator lens, and compute a focusing direction and an amount of unfocus, to immediately obtain an in-focus state. In recent years, a focus detection sensor is formed as a general-purpose module. Thus, a digital still camera has been downsized, the cost of manufacturing a digital still camera has been lowered, and the performance of a digital camera has been more stabilized.
A hybrid video camera has been marketed which uses the TVAF function for normal auto focusing and an inexpensive separate focus detection sensor module for moving a focusing lens to an in-focus position at a high speed in the case where the degree of blurring is high.
In a method discussed in Japanese Patent Application Laid-Open No. 08-146287, a focus detection sensor module is disposed inside a lens hood so as to eliminate parallax between an optical element and a range-finding area of the focus detection sensor.
In a conventional method, it is difficult to mount a lens hood on an optical apparatus with high accuracy because a focus detection sensor module is disposed inside a lens hood. Thus, it is difficult to align a range-finding area with a shooting area with high accuracy. Furthermore, it is necessary to provide an electrical contact between a focus detection sensor and a lens barrel in order to detach a focus detection sensor module together with a lens hood. Thus, in a conventional method, the configuration of the apparatus becomes complicated and it is difficult to stably perform an auto focus (AF) function.